Safety Cabinet Selection
Selecting the proper BSC is determined based on the materials that are planning to be handle in the cabinet. BSC classifications and standards for the United States are set by NSF International (formerly the National Sanitation Foundation). NSF defines four types of Class II cabinets (A1, A2, B1 and B2) that are distinguished by differences in airflow patterns and velocities, HEPA air filter positions, ventilation rates and exhaust methods. 

The three main types of biosafety cabinets are Class I, Class II, and Class III, with the most common type of biosafety cabinet used for biohazards is the Class II Type A2.

Type I Biosafety Cabinets
Class I cabinets provide personnel and environmental protection by filtering air through a HEPA filter before it is exhausted. These cabinets do not protect the product within from potential contamination and are suitable for general manipulations of low-to-moderate risk agents where product sterility is not a priority.

Type II Biosafety Cabinets

Protection

• Personnel protection from harmful agents used inside the biosafety cabinet.
• Product protection to avoid contamination of the work, experiment, or process from outside contaminants.
• Environmental protection from contaminants contained within the biosafety cabinet.

Key Features

• A front access opening with carefully maintained inward airflow.
• HEPA-filtered, vertical, unidirectional airflow within the work area.
• HEPA-filtered exhaust air to the room or exhaust to a facility exhaust system.

Applications
Type A1 and A2 cabinets are typically used for biosafety levels 1 through 3. Because Type A1 cabinets are not suitable for work with chemicals, use of Type A2 cabinets is more prevalent.  As long as vapors are not hazardous and will not interfere with the work when recirculated, it is acceptable to use an A2 cabinet with a small amount of chemicals when the cabinet is exhausted to the outdoors for removal of gases.  

Type B1 and B2 cabinets are also typically used for biosafety levels 1 through 3.  As with type A2 cabinets, type B1 cabinets can be used for work generating chemical vapors as long as the vapors do not interfere with the work when recirculated or when the work is done in the directly exhausted portion of the cabinet. The type B2 total exhaust cabinets are widely used in toxicology laboratories and similar applications where chemical effluent is present and clean air is essential.  

Specifics

• Type A1 BSCs
  Often used in clinical and research laboratories for standard microbiological work with no chemical evaporation. Type A1 cabinets maintain a minimum inflow velocity of 75 feet per minute and recirculate 70% of the air while exhausting 30% outdoors after filtration. They are not suitable for handling volatile or toxic chemicals.
• Type A2 BSCs
  Similar to Type A1 but with increased inflow velocity of 100 feet per minute, enhancing containment. Type A2 cabinets can handle minute amounts of volatile chemicals if vented with an appropriate thimble (canopy) connection to the facility’s HVAC system. This type is prevalent in pharmaceutical compounding and biotechnology sectors.
• Type B1 BSCs
  Designed for work involving minute quantities of toxic chemicals and radionuclides as long as these operations occur toward the rear of the work area, directly exhausted outside. Type B1 maintains a balance where 70% of air is exhausted and 30% is recirculated, both through HEPA filters.  
• Type B2 BSCs
  Also known as Total Exhaust Cabinets, these are suitable for handling significant quantities of toxic chemicals and radionuclides. They maintain a minimum inflow of 100 feet per minute and exhaust 100% of the air. All inflow and downflow air is ducted out of the building, providing no recirculation within the cabinet.

HEPA filters capture particulates/aerosols, but do not trap chemical vapors/gases.  Therefore, any chemical vapors are exhausted into the lab unless the BSC is connected to the building’s exhaust ventilation system (you would see a duct ‘attached’ to the exhaust HEPA at the top of the cabinet, and for thimble connections, there is an additional alarm to detect if the building exhaust is not functioning normally.) 

For energy efficiency, Class II Type A2 BSCs recirculate the air blown onto the work surface.  Any volatile chemicals are continuously recirculated and therefore, concentrated in the work surface.  If flammable chemicals are used, the Lower Explosive Limit can be reached.  

Additional options for biosafety cabinets include ultraviolet (UV) lights for the work surface and natural gas connections. 

• Ultraviolet (UV) light can burn skin and eyes and damage materials left in the cabinet. Lab personnel must also keep the bulbs dust-free and make sure the wavelength and output is checked once a year.
• Natural gas hook-ups should not be used for Bunsen burners. Flames can damage the HEPA supplying sterile air to the work surface and can cause significant fires (especially if flammables such as ethanol are used on the work surface, due to air recirculation in Class II Type A2 BSCs).  

BSCs serve as engineering controls in OSHA’s hierarchy of controls and as primary containment for the CDC/NIH. 

BSCs are commonly referred to as ‘hoods’ in the lab, but ‘hood’ is a more general term that refers to BSCs, chemical fume hoods, clean benches, PCR hoods, vertical laminar flow hoods, etc. While a ‘hood’ is any enclosed work surface with controlled airflow that personnel can place their arms in and perform experiments, each type is designed differently based on the use or hazards to control.  Therefore, lab personnel must know what hazards they work with and what ‘hood’ to use or not use.

• The proper use of a BSC compliments good microbiological techniques and results in effective containment and control of infectious agents. As with any other piece of lab equipment, personnel must be trained in its proper use.
• Read the manufacturer’s Operator’s Manual so you know the specific features and alarms unique to your BSC. The BSC manufacturer and model number will be on the BSC.
• Chemicals must not be used in a biological safety cabinet (BSC) and should only be used in a chemical fume hood. Most BSC types blow the HEPA-filtered air back into the room and will not trap chemicals in vapor form. Small amounts of chemicals common to biological research (e.g. TRIzol) may be used and chemical bottles must be closed when not in use. Contact the EHS for a risk determination before using a volatile or toxic chemical in a BSC.
• Flammable materials should not be used in a BSC. Most BSC types recirculate the air within the cabinet, which can concentrate chemicals. Flammable chemicals like ethanol can get into the explosive concentration range (Lower Explosive Limit) and cause a fire within the cabinet. Even if there is no explosion risk, flames may damage the HEPA filters.
• Before every use, the BSC must be decontaminated to prevent cross-contamination. Occasionally clean and decontaminate the space below the work surface, accumulating broken glass, spilled materials, and general gunk. Use tongs to remove broken glass. Establish a regular schedule to perform this activity, perhaps once or twice a year and as needed.
• When a BSC needs repaired, different groups are responsible for the repairs. The outside vendor that certifies the BSC is responsible for all repairs inside the cabinet. This would include the motor(s), HEPA filter(s), or any potentially contaminated surfaces inside the cabinet. The RPI facilities team is responsible for any repairs outside of the BSC, which would include building ventilation and electrical supply.

Creating a Safe Working Environment in Your BSC

Since the primary purpose of a BSC is to capture particulates and aerosols from biohazardous or infectious agents, existing BSCs must be decontaminated prior to being moved. 

Relocation Steps:

1. Lab members contact EHS to schedule a BSC decontamination. The decontamination will be performed by RPI’s approved vendor.
2. Prior to vendor’s arrival, lab members should remove all materials from the BSC and perform a surface decontamination of interior workspace of the BSC with an appropriate disinfectant.
3. Vendor performs fumigation procedure. Once complete, vendor places a decontamination sticker on the BSC.
4. EHS will place a clearance tag on the BSC and then the BSC can be moved.
5. Once the BSC has been relocated and placed in its new location, the BSC should be re-certified by RPI’s approved vendor and EHS records should be updated to reflect the BSC’s new location.